Mass spectrometry (MS) is an exceptionally powerful tool for chemical analysis. However, separating ions by mass will not always provide a unique signature, thus there is an ongoing demand for complementary orthogonal chemical separation methods that can be used in series with MS to aid in analysing complex mixtures.
High Pressure Liquid Chromatography (HPLC) is a technique which separates chemical mixtures based upon their physical shape and chemical functionality in solution. HPLC is often used in combination with electro-spray ionisation to pre-separate ions for further analysis via MS creating a technique known as liquid chromatography mass spectrometry (LCMS). However, even such complex techniques as LCMS cannot always uniquely identify elements in complex mixtures.
Field asymmetric ion mobility spectrometry (FAIMS) separates gaseous ions based upon their physical shape and chemical functionality in the gas phase and has previously been used as a pre-separator for MS. However, previous FAIMS systems designed for interfacing to mass spectrometers have been large, cumbersome and expensive. Such systems have also been unable to apply the highest FAIMS electric fields due to their large ion channel widths, and have also been poorly configured to couple ions effectively from the output of the FAIMS device to the MS. In addition, prior art FAIMS MS systems have been relatively slow when ideally the FAIMS device should carry out the separation on timescales commensurate with typical mass spectrometry experiments (for example, full sweeps within the duration of typical LC peaks which could be down to 1 second long, or able to step compensation voltages (CVs) to different points fast enough for Multiple Reaction Monitoring (MRM) type experiments where different ions are targeted by the mass spectrometer in sequence, with potentially up to approximately 500 ions per second being examined).
Additionally, since it is desirable for a FAIMS device to fit between the ionization source and the inlet to the mass spectrometer, it should be small and movable. Additionally, a FAIMS filter downstream of an electro spray ionization source should be configured such that it can be easily cleaned or replaced (minimizing system down time) such as when it becomes contaminated with electrospray residue which tends to occur downstream of an electrospray ionization source.